This invention relates to rolling mills and methods of rolling metal in rolling mills.
It is customary in rolling mills to apply a coolant to the rolls and/or the work to hold the temperature of the work within reasonable limits regardless of the heat generated during rolling. The coolant is usually water or is water-based, and includes a rolling lubricant; an oil-water emulsion is frequently employed.
When water-based coolant contacts aluminium strip, it reacts with the aluminium to cause staining of the strip surface, which may inhibit the action of the rolling lubricant, even if applied separately from the coolant. The result is that the reduction effected in the mill is non-uniform across the strip width so that strip with poor flatness is produced. Further, the hardness of the stained areas differs from that of the remainder of strip and that causes unequal reduction in any subsequent rolling operation and further loss of flatness. Lastly, the appearance of the rolled material is marred.
In British patent specification No. 1511247, corresponding to U.S. Pat. No. 3,994,151, it has been proposed to confine the application of coolant, which preferably contains rolling lubricant, to the rolls, no coolant being directed on to the work. The coolant is applied to the rolls at the outgoing side of the mill by nozzles which are enclosed in casings sealed to the work rolls and their back-up rolls by the use of air seals. Lubricant contained in the coolant is said to be transferred to the ingoing side of the mill, and thence to the roll gap, through the nip between each work roll and its back-up roll.
Air seals were employed, evidently because contact seals engaging the work rolls, in particular, were likely to cause damage to the roll surface and hence to the strip. Also the seals would be unable to withstand the high temperature and dryness of the work rolls leaving the roll bite. However, air seals can create a water mist which may escape from the casings adjacent the roll bite and contaminate the rolled product. More importantly, coolant is carried over to the ingoing side of the mill through the work roll/back-up roll bites and delivered by the work rolls to the work at the bite between the work rolls. Consequently, the strip is again contaminated with the disadvantages mentioned above.
The British specification also has a FIG. 3 which shows the rolls at each side of the pass-line enclosed in a casing and coolant/lubricant applied at both the ingoing and the outgoing sides of the mill. Gaps are left between the casings and the work rolls at the roll bite and, according to the provisional specification, the interior of each casing is evacuated with the intention of preventing coolant passing through the gaps to the rolled material. It would however be impossible in practice to obtain in the casings sufficiently low pressures to remove from the work rolls coolant retained thereon by surface tension. Coolant would be carried by the work rolls into the work-roll bite and thence delivered to the surfaces of the strip.
The arrangements illustrated in the British specification would fail to give proper lubrication at the roll bite. If the lubricant is incorporated in the coolant, there are the dangers of it being inadequately distributed uniformly throughout the coolant and of non-uniform lubrication at the bite: if it is delivered separately from the lubricant, its effectiveness at the roll bite may be non-uniform because of the wetting of the work by the coolant as described above.